1. Technical Field
The present invention relates to a semiconductor device and a method for manufacturing a semiconductor device.
2. Background
Memory devices storing information such as digital information are commonly used in electronic apparatuses. DRAMs, one type of memory device, typically comprise millions of identical circuit elements, known as memory cells, which can be charged to a voltage representative of a digital data value.
FIG. 1 depicts a schematic diagram of a conventional DRAM memory cell 10. The memory cell 10 has a capacitor 12 and a transistor 14. The capacitor 12 can store charge, which represents one bit of information. The transistor 14 acts as a switch, which controls the flow of charge in or out of the capacitor 12. The control gate of the transistor 14 is coupled to a word line 16, and the drain of the transistor 14 is coupled to a digit line 18. When a cell is read, the transistor 14 is activated through the word line 16, and the charge in the capacitor 12 can be detected by a sense amplifier through the digit line 18 and processed to determine the bit state of the cell 10. Arranging a plurality of cells 10 together, such that the cells 10 along a given digit line 18 do not share a common word line 16 and the cells 10 along a word line 16 do not share a common digit line 18, forms a memory array. A typical memory array contains thousands or millions of cells.
As the size of memory devices decreases, the components of the devices become smaller and/or denser for a given storage capacity. Small DRAMs can be formed using a buried word line technology. Such technology generally forms a trench, and a word line is then formed in the trench. Oxide is usually applied to isolate the word line. Subsequently, digit lines are formed and an insulating layer is etched to form a plurality of cell contact holes. Conventionally, the oxide isolating the word line is not properly protected; therefore, the oxide may be damaged, or keyholes or etched holes may be formed on the oxide during an etch process.